Fix sp in Week3-derivativeSign.html
Another sp in differentiateUsingLimit.html

From upstream, it looks like.
Fix some errors on README and add Linux instructions

This can be split if you don't want the Linux patch. But it looks pretty
unintrusive to me.
Rebase: Week 1+2 graphical limits: Change stated epsilon from fraction to decimal

Since only decimal answers are accepted by the grader, using a fraction as
an example is confusing.

Update: This has been rebased and now fixes all instances of this confusion in
Weeks 1&2.
correct answer for 5.2#8
productRuleTwoWays: Change first hint to actually be a hint

The first hint was simply the text "Let's do Method 1 first:". So you had
to click the hint button twice to see any hints. Very trivial, I know.
Fixed typo
Merge branch 'development' of github.com:ASCTech/mooculus into development
Merge branch 'development'
Fixed plurals of max and min
Merge branch 'development'
fixed some video links
Merge branch 'development' of github.com:ASCTech/mooculus into development
Merge branch 'development'
Fixed parentheses in ultimate differentiation challenge
Merge branch 'development'
Merge pull request #66 from mateor/dev2

Week2: Fix some front-facing spell errors
Merge branch 's5.2#8' of https://github.com/clark-archer/mooculus into development
Merge branch 'development' of github.com:ASCTech/mooculus into development
Merge pull request #68 from clark-archer/s5.2#8

correct answer for 5.2#8